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On 04/01/2010 01:11 AM, Nathaniel Iwuchukwu wrote:
<blockquote
cite="mid:j2k2336bcfa1003311511t7aacf695g19994cc877725882@mail.gmail.com"
type="cite">
<div>Thanks Micha,</div>
<div>I ran r.thin and got just one line. is there a way i can improve
it?<br>
<br>
</div>
</blockquote>
Good, so we're making progress...<br>
How many polygon areas did you create in the training map? Does it
cover various portions of the roads?<br>
<blockquote
cite="mid:j2k2336bcfa1003311511t7aacf695g19994cc877725882@mail.gmail.com"
type="cite">
<div class="gmail_quote">On Wed, Mar 31, 2010 at 1:54 PM, Micha
Silver <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:micha@arava.co.il">micha@arava.co.il</a>></span> wrote:<br>
<blockquote
style="border-left: 1px solid rgb(204, 204, 204); margin: 0px 0px 0px 0.8ex; padding-left: 1ex;"
class="gmail_quote">
<div class="im">Nathaniel Iwuchukwu wrote:<br>
<br>
<blockquote
style="border-left: 1px solid rgb(204, 204, 204); margin: 0px 0px 0px 0.8ex; padding-left: 1ex;"
class="gmail_quote">Also, when i convert from vector to raster, i
don't see anything on the new raster map. its all blank. what should i
do. thanks<br>
</blockquote>
</div>
I guess that would explain why you're getting "Training map has no
classes".<br>
Can you display the vector which covers sections of the road? Do you
see filled polygons?<br>
If not maybe you made boundaries with no centroids? In GRASS, area
features must be composed of both a boundary *and* a centroid. In the
digitizer there's a special button for adding a centroid. You need one
inside each polygon boundary.<br>
<br>
<blockquote
style="border-left: 1px solid rgb(204, 204, 204); margin: 0px 0px 0px 0.8ex; padding-left: 1ex;"
class="gmail_quote">
<div class="im"><br>
On Wed, Mar 31, 2010 at 11:20 AM, Nathaniel Iwuchukwu <<a
moz-do-not-send="true" href="mailto:ikechinedu@gmail.com"
target="_blank">ikechinedu@gmail.com</a> <mailto:<a
moz-do-not-send="true" href="mailto:ikechinedu@gmail.com"
target="_blank">ikechinedu@gmail.com</a>>> wrote:<br>
<br>
Thanks Micha,<br>
I will definately post it once i scale through it.<br>
i am getting an error when i run the i.gensigset on the training
data.<br>
this is what i typed and the result:<br>
GRASS 6.4.0RC5 (sis):~/Desktop > i.gensigset trainingmap=traingis<br>
group=sislabgp subgroup=sislabsub signaturefile=sislab.sig<br>
Finding training classes...<br>
100%<br>
ERROR: Training map has no classes<br>
do you have any clue why i don't have a class?<br>
Thanks Man<br>
</div>
2010/3/31 Micha Silver <<a moz-do-not-send="true"
href="mailto:micha@arava.co.il" target="_blank">micha@arava.co.il</a>
<mailto:<a moz-do-not-send="true" href="mailto:micha@arava.co.il"
target="_blank">micha@arava.co.il</a>>>
<div class="im"><br>
<br>
On 03/31/2010 01:19 AM, Nathaniel Iwuchukwu wrote:<br>
<blockquote
style="border-left: 1px solid rgb(204, 204, 204); margin: 0px 0px 0px 0.8ex; padding-left: 1ex;"
class="gmail_quote"> Thanks Micha,<br>
this looks good but am still working on it. would you know<br>
the RGB for a road? from the link you<br>
</blockquote>
No, I can't tell what the RGB values for a road would be, and<br>
it will change from image to image, and from road to road.<br>
<blockquote
style="border-left: 1px solid rgb(204, 204, 204); margin: 0px 0px 0px 0.8ex; padding-left: 1ex;"
class="gmail_quote"> sent me, i will need it to capture the
pixel values of road<br>
polygons that i am digitizing.<br>
</blockquote>
You *don't* need to find the actual pixel values for the road<br>
polygons. You just digitize strips that cover the road, and<br>
feed these areas (after converting to a raster) as the<br>
training map. The gensigset module creates the collection of<br>
pixels values that match "roads"<br>
<br>
<blockquote
style="border-left: 1px solid rgb(204, 204, 204); margin: 0px 0px 0px 0.8ex; padding-left: 1ex;"
class="gmail_quote"> thanks Micha. you really gave me a lead.<br>
</blockquote>
Good. Post back to the list when you get it worked out.<br>
<br>
<br>
</div>
<blockquote
style="border-left: 1px solid rgb(204, 204, 204); margin: 0px 0px 0px 0.8ex; padding-left: 1ex;"
class="gmail_quote">
<div class="im"> Nathaniel<br>
<br>
On Tue, Mar 30, 2010 at 4:26 PM, Micha Silver<br>
</div>
<div>
<div class="h5"> <<a moz-do-not-send="true"
href="mailto:micha@arava.co.il" target="_blank">micha@arava.co.il</a>
<mailto:<a moz-do-not-send="true" href="mailto:micha@arava.co.il"
target="_blank">micha@arava.co.il</a>>> wrote:<br>
<br>
Nathaniel Iwuchukwu wrote:<br>
<br>
sorry my typo. i mean classification.<br>
<br>
I didn't intend to insult. Sometimes typos come out<br>
funny, and I can't resist pointing it out...<br>
<br>
but am looking for procedure on road extraction from<br>
satellite imagery with high resolution<br>
<br>
OK, you'll probably want to use "supervised"<br>
classification. This means giving the classification<br>
algorithm a "training" layer. So the process involves<br>
1- First create a vector layer using the grass digitizer<br>
with small polygons covering some sections of the roads<br>
in the satellite image. Convert the vector to a raster<br>
(v.to.rast). This will be the training map.<br>
2- Now group the satellite bands into an imagery group<br>
(i.group)<br>
3- Run i.gensigset with the training raster and the<br>
imagery group.<br>
4- Now use i.smap with the signature file and imagery<br>
group as input, and a classification map as output.<br>
5- If the results look good, run r.thin on this raster,<br>
and then r.to.vect to see what you get.<br>
<br>
Here's a more detailed explanation that you might find<br>
helpful:<br>
<a moz-do-not-send="true"
href="http://www.surfaces.co.il/?p=3" target="_blank">http://www.surfaces.co.il/?p=3</a><br>
<br>
Regards,<br>
Micha<br>
<br>
<br>
</div>
</div>
</blockquote>
<div>
<div class="h5"><br>
-- Micha Silver<br>
<a moz-do-not-send="true" href="http://www.surfaces.co.il/"
target="_blank">http://www.surfaces.co.il/</a><br>
Arava Development Co. +972-52-3665918<br>
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</blockquote>
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-- <br>
<font color="#888888">Micha Silver</font>
<div class="im"><br>
Arava Development Co. +972-52-3665918<br>
</div>
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<div class="h5"><a moz-do-not-send="true"
href="http://www.surfaces.co.il/" target="_blank">http://www.surfaces.co.il</a><br>
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<pre class="moz-signature" cols="72">--
Micha Silver
<a class="moz-txt-link-freetext" href="http://www.surfaces.co.il/">http://www.surfaces.co.il/</a>
Arava Development Co. +972-52-3665918</pre>
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